Several authors in both major oil companies and major equipment suppliers have promulgated the use of optimized drilling oil and gas wells rate of penetration (ROP) with a system that attempts to measure the mechanical specific energy (MSE) of the drilling process.
The concept of MSE in rock drilling was formulated by Teale in the 1960's and has been used by several drill bit manufactures as a measure of drilling efficiency. Two operators made significant progress in increasing drilling rates using an MSE based system on oilfields in Qatar. The significant accomplishment of this process was a faster rate of penetration of 20-250% as seen in hole sizes from 17½ inch to 8½ inch in vertical and build sections, with the greatest improvement in the 17½ vertical section.
The use of MSE as promulgated by another author Dupriest, involves both technology and workflow. Regarding the technology, MSE is calculated continuously by a data acquisition system supported by information from either surface equipment or downhole tools such as a measurement-while-drilling (MWD) downhole tool and a vibration sensor tool. In addition, sometimes rock characteristics (and associated bit aggressiveness) is used as information in assessing downhole drilling performance, which is usually done offline to the drilling process. The information is then displaced to the drilling operator who intervenes in the process by making adjustments to the drilling process, usually adjusting the weight on bit (WOB). Other adjustments include changing the RPM or increasing the hydraulic specific energy (mud flow rate).
The inherent limitations of the system described above are 1) when relying on surface measurements, no direct measurement of the effects from the drill string to the formation and casing are included, thus potentially masking downhole problems, 2) when using downhole equipment for measurements, the time delay from instrumentation measurement to operator response (assuming he knows the correct response), and 3) significant expense in training, equipment, system monitoring of the process, especially the workflow process.
Consequently a need exists for a self-contained, automatic feedback, real time, downhole assembly that provides optimization of the ROP via the control of the MSE. The present invention circumvents the limitations above and offers the opportunity for all the benefits of increased ROP resulting in less drilling cost per well.